In mining, more than any other industry, there is a lack of conformity with regard to the processes, machinery and equipment which are utilized as well as in the resulting products which militates against standardization and the application of automated processes and machinery. However, in common with many other heavy engineering activities, mining is essentially a large scale exercise in material handling, albeit of a complexity probably much greater than in any other industry. Thus, not only must large tonnages of minerals and ores be moved for distances up to fifteen kilometers or more underground, but also provision must be made for ventilation air and its circulation, and this and the water handling systems involved may require much greater energy than the haulage of the rock and ores.
Moreover, in mines at depths between 3,500 and 4,000 meters below the surface, virgin rock temperatures may be as much as 65.degree. C. Under such temperature conditions, it is virtually impossible for ventilation air, as such, to provide sufficient cooling, but rather it is used as a medium for absorbing and conveying the unwanted thermal energy from the site. A temperature of 28.degree. C. wet bulb, considered the maximum for sustained operations in such mines, can only be maintained by providing refrigeration to the ventilation air at the working level and particularly at the working site. In existing mines at this depth, the refrigeration is provided in several different fashions. Basically, the air is conveyed through at least two bulk air coolers, wherein the air is cooled by water chilled to as low as 0.5.degree. C. at the mine's surface. Ice machines may be used in conjunction with such a system. Pelton wheels are frequently strategically incorporated into the system, coupled to induction generators to produce electric power fed back into the mine's electrical network. Water introduced into the mine for various purposes is pumped to the surface by high lift pumps.
Concerning refrigeration systems for cooling the chilling water, ammonia systems that place the evaporator at or near the working level within the mine would, in theory, be of considerable advantage in that the power consumption is relatively low and the design is relatively simple. Unfortunately, the use of ammonia as a refrigerant within the mine entails safety aspects, and thus is generally avoided.
In any consideration of the ventilation system for deep-level mines, the problems of adjusting to existing mine layouts and equipment must be considered. Included are problems associated with providing wholesome air to the underground workers, diluting exhaust fumes from diesel-fueled trackless equipment, carrying away dust created by blasting and other mining operations, and the need to optimize operational assets to achieve maximum efficiency. Existing systems may have three-chamber pipe feeders, wherein the vertically descending chilled water from the surface refrigeration plant is utilized to assist lifting warm service water to the surface.
Further, as indicated above, in deep-level mines, the average face temperature is invariably unacceptably high without provision for underground cooling, which is normally obtained by chilled water, but may be augmented by the introduction of ice. To maintain the temperature less than an operational maximum of about 27.degree. C. or 28.degree. C. wet bulb, eventually the water flow consumption to meet the requirements of bulk air cooling becomes unacceptable, depending largely upon the depth of the mine and the amount of excess thermal energy that must be removed.
Other parameters which should be taken into account in designing ventilation air and water systems for deep-level mines include the friction heating of both water and air which must be conducted to the working levels. In addition, there is a significant adiabatic increase in air temperatures due to the increased pressures at lower levels, and the temperature of the rock also increases with the depth of the mine. Thus, even with high grade ores, a currently accepted point of diminishing returns is reached at a depth of about 4,000 meters. This includes providing for the additional use of ice, which is transported to the working level, or to intermediate working level, to enhance the cooling effect of existing ventilation air systems.
Technical problems relating to air ventilation and in deep-level mining are covered in some detail by articles presented at the International Deep Mining Conference in Johannesburg, SAIMM, 1990, published within TECHNICAL CHALLENGES IN DEEP-LEVEL MINING, pages 1323-1396:
Ventilation and Refrigeration Considerations in the Design of a Deep/Hot Gold Mine Using Trackless Operations, by A. M. Patterson, p. 1323;
Refrigeration Systems for a Deep-Level Mine, by F. Lloyd and J. P. Cronje, p. 1333;
The Optimal use of Thermal Insulation for Chilled Water Pipes in Mine Cooling Systems, by R. Ramsden, H. J. M. Rose and B. J. Wernick, p. 1339;
Ventilation and Refrigeration Requirements for a Semi-Mechanized Mining Method at Freecold North--No. 1 Shaft Project, by D. H. Hoffman and J. D. Wessels, p. 1347;
The Development of a Refrigeration System at Depths Between 3,500 and 4,000 Meters Below Surface, by P. J. Jansen van Rensburg, p. 1357;
Ventilation Arrangement for Merensky Reef Exploitation Below 1,000 m Depth at Rustenburg Platinum Mines Ltd--Union Section, by D. J. Stanton and G. A. C. Viljoen, p. 1365;
An Assessment of the Energy Requirements for Deep-Level Mine Cooling, by D. Dawes, P. G. Lloyd and J. J. E. A. Francen, p. 1373.
These articles are incorporated by reference herein.